Large inter-individual and intra-individual variability in the effect of perceptual load.

Hadas Marciano,Yaffa Yeshurun,Leonardo Chelazzi

doi:10.1371/journal.pone.0175060

Abstract

This study examined whether the recurrent difficulty to replicate results obtained with paradigms measuring distractor processing as a function of perceptual load is due to individual differences. We first reanalyzed, at the individual level, the data of eight previously reported experiments. These reanalyses revealed substantial inter-individual differences, with particularly low percentage of participants whose performance matched the load theory’s predictions (i.e., larger distractor interference with low than high levels of load). Moreover, frequently the results were opposite to the theory's predictions–larger interference in the high than low load condition; and often a reversed compatibility effect emerged–better performance in the incompatible than neutral condition. Subsequently, seven observers participated in five identical experimental sessions. If the observed inter-individual differences are due to some stable trait or perceptual capacity, similar results should have emerged in all sessions of a given participant. However, all seven participants showed large between-sessions variations with similar patterns to those found between participants. These findings question the theoretical foundation implemented with these paradigms, as none of the theories suggested thus far can account for such inter- and intra-individual differences. Thus, these paradigms should be used with caution until further research will provide better understanding of what they actually measure.

Highlights

The perceptual load theory claims that perceptual load is one of the major factors determining the selectivity of attention [1, 2]
In each of Experiments 1, 2a, 2b and 3 a larger distractor interference emerged under high level of perceptual load with the accuracy measurement
According to the perceptual load theory, the magnitude of distractor interference should be larger with low than high levels of load; it predicts that all data points should fall below the diagonal of equal magnitude

Summary

Introduction

The perceptual load theory claims that perceptual load is one of the major factors determining the selectivity of attention [1, 2]. With Experiment 4, in which the number of possible distractor locations was reduced from 10 to 2, the pattern of results expected by the load theory was replicated Based on these findings we concluded that high levels of perceptual load increase attentional selectivity only when there is minimal uncertainty regarding the spatial location of the distractor [3]. In three out of the four experiments (Experiments 2–4, inverse efficiency scores, for a full description of the relevant results see Appendix B in S1 File) of that later study we once again found larger distractor interference under high than low levels of load, even though there were only two possible distractor locations This large distractor interference with high levels of load could not be attributed to high spatial uncertainty. If the manner by which perceptual load affects the magnitude of distractor interference depends on some structural factor or any stable personal trait (e.g., working memory capacity), a consistent pattern of results should be found for a given participant across all sessions

Part I: Analysis of individual differences

Results and discussion

Part II: Within-participant variability